Chandra detections of SCUBA galaxies around high-z radio sources

The most massive galaxies in the present-day universe are the giant elliptical galaxies found in the centers of rich clusters. These have old, coeval stellar populations, suggesting they formed at high redshift, and are expected to host supermassive black holes (SMBHs). The recent detection of several high-redshift radio galaxies (HzRGs) at submillimeter wavelengths confirms that some massive galaxies may indeed have formed the bulk of their stellar populations in spectacular dust-enshrouded starbursts at high redshift. In this paper we compare sensitive Chandra X-ray images-which identify actively fueled SMBHs-and submillimeter observations-capable of detecting obscured activity in luminous galaxies at high redshift-of the environments of three HzRGs. These observations exhibit overdensities of X-ray sources in all three fields and a close correspondence between the Chandra and submillimeter populations. This suggests that both substantial star formation and nuclear activity may be occurring in these regions. We identify possible pairs of Chandra sources with each of two submillimeter sources, suggesting that their ultraluminous activity may be triggered by the interaction of two massive galaxies, each of which hosts an accreting SMBH. The presence of two SMBHs in the resulting remnant is predicted to produce a flattened stellar core in the galaxy, a morphological signature frequently seen in luminous cluster elliptical galaxies. Hence, the confirmation of pairs of Chandra sources within individual, luminous submillimeter galaxies would provide additional evidence that these galaxies at z similar to 2-4 are the progenitors of the giant elliptical galaxies found in clusters at the present day.